Recently, with miniaturization and higher density of electronic equipments, a double-sided, multi-layer substrate is being more widely used than a conventional one-sided substrate for a circuit forming substrate for mounting electronic components, and a high density substrate in which a greater number of circuits and components can be integrated on a substrate have been developed.
FIG. 8A to FIG. 8E show manufacturing steps of the conventional circuit forming substrate. As shown in FIG. 8A, circuits 27a, 27b are respectively formed on one main surface and other main surface of core substrate material 21, individually. FIG. 8A shows a double-sided substrate formed with inter-layer connecting part 23 by conductive paste. Note that a multi-layer substrate may also be used other than the double-sided substrate. In addition to the conductive paste, various methods such as plating, soldering, or the like can be adopted for inter-layer connecting part 23.
Prepregs 22L and 22U are then arranged on the top and the bottom thereof so as to sandwich core substrate material 21, as shown in FIG. 8B. Conductive pastes 23a1, 23a2, 23b1 and 23b2 are arranged in via holes 24 of prepregs 22L, 22U. Copper foil 26L that is a first metal foil and copper foil 26U that is a second metal foil are respectively arranged on prepreg 22L side and 22U side. Since prepregs 22L, 22U contain half-cured resin, cooper foils 26L, 26U and prepregs 22L, 22U or prepregs 22L, 22U and core substrate material 21 are partially temporary pressure bonded with heater tool and the like in positioning. The positional shift in subsequent handling is thereby prevented.
Heat and pressure are then applied by the heat press device (not shown) to cure prepregs 22L, 22U to be integrated with core substrate material 21, as shown in FIG. 8C. Conductive pastes 23a1, 23a2, 23b1, and 23b2 are also compressed and cured, thereby exerting conductivity and electrically connecting the layers.
The extra portions at the end face of the circuit forming substrate are then cut to obtain a four-layer circuit forming substrate as shown in FIG. 8D, copper foils 26L, 26U at the surface are etching processed to form circuits 26L1, 26U1, and the four-layer circuit forming substrate as shown in FIG. 8E is obtained.
Depending on the application, solder resist for soldering is applied to the surface of the circuit forming substrate shown in FIG. 8E or gold plating or surface processing such as flux processing or soldering lever is performed on the surface of circuits 26L1, 26U1. Subsequently, the substrate is cut to the desired sheet size with a die, rooter process, or the like and provided to the circuit forming substrate in the assembly step of the electrical equipment and the like. Japanese Patent Publication, Japanese Patent Un-examined Publication No. H06-268345 is known as the conventional art document information related to the invention of the subject application.
However, in the method for manufacturing the circuit forming substrate described above, manufacturing constraints are restricted when attempting to increase the size of prepregs 22L, 22U. That is, jigs and the like cannot be contacted to prepregs 22L, 22U since non-cured conductive paste 23a1, 23a2, 23b1, and 23b2 are arranged. If contacted, the conductive paste spreads to the periphery, whereby drawbacks arise, for example, electrical short between the circuit and another circuit occurs or the reliability of inter-layer connection lowers.
Prepregs 22L, 22U must be stored in a hollow supporting jig so that conductive paste 23a1, 23a2, 23b1, and 23b2 are not damaged from the outside. When handling prepreg 22L, 22U during a stacking step, only the end faces thereof can be gripped, and thus is subjected to manufacturing constraints. The difficulty in handling task in the stacking step becomes higher as the size of prepregs 22L, 22U becomes larger. Thus, the reliability of the quality also becomes unreliable in terms of manufacturing the circuit forming substrate.
Furthermore, since positioning with circuits 27a, 27b on core substrate material 21 becomes difficult when the positions of conductive pastes 23a1, 23a2, 23b1, and 23b2 arranged in prepregs 22L, 22U vary, correspondence to miniature circuit forming substrate is difficult. The variation in the position of conductive paste 23a1, 23a2, 23b1, and 23b2 thus cannot be ignored as the size of prepregs 22L, 22U increases.
In order to reduce the manufacturing cost of the circuit forming substrate, on the other hand, increasing the size of prepregs 22L, 22U, that is, the work size in manufacturing is effective in terms of production efficiency. Thus, embodiment of a manufacturing method for stably manufacturing the circuit forming substrate having a large work size is desired.